This invention relates to portable, battery-operated infrared transmitters such as, for example, IR badges and IR remote control devices.
The principle of operation of IR transmitters in IR badges and remote control devices, for example, is that modulated data may be transmitted by an IR LED array so that the light signal transmitted thereby may be received by an IR receiver in line-of-sight relationship with the IR transmitter. The range of such devices is thus a function of the light energy emitted by the LED array in the IR transmitter and this, in turn, depends on the battery voltage. Since portable IR transmitters are, by their very nature, powered by an internal battery this means that the signal strength tends to become weaker as the battery discharges. This, in turn, results in the range of the transmitter decaying as the battery ages, thus requiring, that the IR transmitter be brought into closer proximity to the IR receiver in order to be effective or, alternatively, that the battery be replaced even before the end of its effective lifetime. Neither alternative is ideal.
Yet another even more serious drawback relates to the fact that, in order to allow for effective IR transmission over the desired range of approximately of 30 m, the currents flowing through the diodes in the LED array must be relatively high. Since such devices are by their nature used to transmit very short intermittent bursts of data, the design is based on charging capacitors during the time interval between transmissions, whereby upon transmission the capacitors are discharged giving rise to relatively high currents which are significantly larger than the short circuit current of the battery. During discharge of the capacitor, the voltage across the capacitor falls and so too, therefore, does the transmission power, which is thus not constant even during transmission of a short pulse. This gives rise to serious problems in implementation.
It is therefore an object of the present invention to provide a battery operated IR transmitter comprising at least one IR LED energized by a source of voltage for passing current during transmission of pulses of data, said IR transmitter including an energy regulator for maintaining transmission energy through the at least one IR LED substantially constant regardless of fluctuations in said voltage.